The present invention relates to mechanical joints and robot wrists, and in particular, it relates to mechanical joints and robot wrists having compound pitch/yaw motion capabilities.
Interest in robotics and the use of robots in industrial applications has greatly increased in recent years. One area in which the use of robots has become important is the replacement of humans in tasks that involve manual work, such as welding, material handling, paint spraying and assembly. Many of these tasks require working in cramped spaces or performing complex maneuvers. To perform such tasks, a robot arm or wrist should be able to rotationally move in a range similar to a human wrist and at a dwell time acceptable for the particular task involved.
Robot arms, wrists and joints are known in the art. One book reviewing the development of robot arms and wrists is entitled, Robot Wrist Actuators, John Wiley & Sons, Inc., 1989, and was written by the applicant of the present application. In the book, several characteristics are described that make robot wrists attractive. One characteristic is that a mechanical arm or wrist can be safely used in areas where there is a danger of explosion if the wrist is driven by electric actuators. However, there are several disadvantages with the prior art robot arms and wrists. Some of the disadvantages are also enumerated in the above-mentioned article and include large and bulky mechanical joints, singularity-ridden kinematics and low mechanical efficiency.
The Rosheim U.S. Pat. No. 5,036,724, issued to the applicant of the present application, overcame many of the disadvantages mentioned above. The robot wrist of the Rosheim '724 patent describes a mechanical joint having first and second gimbals for effecting pitch and yaw, the first and second gimbals being rotatably attached to a housing support, a yaw drive mechanism in slidable engagement with the housing support, a pitch drive mechanism in slidable engagement with the housing support and a mechanism to actuate the yaw drive mechanism and the pitch drive mechanism. Rollers engaging the surfaces of the yaw and pitch drive mechanisms stabilize the movement of the yaw and pitch drive mechanisms.
The wrist as described in the Rosheim '724 patent was greatly reduced in size compared to the mechanical joints of the prior art. At the same time, dexterity and mechanical efficiency were substantially increased. Over a period of time, however, the adverse conditions under which many of the mechanical joints are operating will affect the rollers which stabilize the movement of the yaw and pitch drive mechanisms. When the rollers are damaged or otherwise impaired by wear or use, the rollers need replacement. Frequent replacement of the rollers increases costs and downtime. Therefore, it is beneficial to maintain stabilization of the movement of the yaw and pitch drive mechanisms without the need for frequent replacement of the stabilizing mechanisms.